Yahoo is claiming that a "state-sponsored actor" is behind the attack, which means a foreign government could be responsible for the data breach. This hack may also have serious implications on the Verizon-Yahoo merger deal that was announced earlier this year.

One of the most frightening things that have come to light with the Yahoo breach is that many people don't realize their information could have been stolen. That's because they may have set up their Yahoo accounts years ago, or used services they didn't realize were associated with the company. Do any of these Yahoo-owned services sound familiar?

With major data breaches like this, more scams are bound to happen. Phishing attacks, mail scams and identity theft are just some of the ways hackers use your information.

That's why it's critical that you lock down all of your online accounts with secure passwords and shut down accounts that are no longer active. The problem is that it's difficult to keep track of all the accounts you have.

A site called AccountKiller makes tracking down all of your online accounts simple.

AccountKiller has a collection of direct links and instructions on how to easily delete your accounts with Facebook, Twitter, Google, Groupon and hundreds of other sites and services. It also uses a color-coding system to tell you at a glance how easy or difficult it is to deactivate your account with each service.

If a site won't let you easily delete your account, AccountKiller will also tell you how to hide your personal data.

Another common mistake people make is using the same passwords for multiple accounts. If you don't know by now, it is bad practice to use the same password across different services.